Ultrasound apparatuses for thermally-induced renal neuromodulation and associated systems and methods

ABSTRACT

Methods and apparatus are provided for thermally-induced renal neuromodulation. Thermally-induced renal neuromodulation may be achieved via direct and/or via indirect application of thermal energy to heat or cool neural fibers that contribute to renal function, or of vascular structures that feed or perfuse the neural fibers. In some embodiments, parameters of the neural fibers, of non-target tissue, or of the thermal energy delivery element, may be monitored via one or more sensors for controlling the thermally-induced neuromodulation. In some embodiments, protective elements may be provided to reduce a degree of thermal damage induced in the non-target tissues.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent application Ser. No. 12/754,337, filed Apr. 5, 2010, which is a continuation of U.S. patent application Ser. No. 11/840,142, filed Aug. 16, 2007, now U.S. Pat. No. 7,717,948, which is a continuation of U.S. patent application Ser. No. 11/504,117, filed Aug. 14, 2006, now U.S. Pat. No. 7,617,005, which claims the benefit of U.S. Provisional Application No. 60/816,999 filed on Jun. 28, 2006. U.S. patent application Ser. No. 11/504,117, filed Aug. 14, 2006, now U.S. Pat. No. 7,617,005 is also a Continuation-In-Part application of each of the following:

(A) U.S. patent application Ser. No. 10/408,665, filed on Apr. 8, 2003, now U.S. Pat. No. 7,162,303, which claims the benefit of U.S. Provisional Application Nos. (a) 60/370,190, filed on Apr. 8, 2002, (b) 60/415,575, filed on Oct. 3, 2002, and (c) 60/442,970, filed on Jan. 29, 2003.

(B) U.S. patent application Ser. No. 11/189,563, filed on Jul. 25, 2005, now U.S. Pat. No. 8,145,316, which is a Continuation-In-Part application of U.S. patent application Ser. No. 11/129,765, filed on May 13, 2005, now U.S. Pat. No. 7,653,438, which claims the benefit of U.S. Provisional Application Nos. (a) 60/616,254, filed on Oct. 5, 2004, and (b) 60/624,793, filed on Nov. 2, 2004.

All of these applications are incorporated herein by reference in their entireties.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

TECHNICAL FIELD

The present invention relates to methods and apparatus for neuromodulation. More particularly, the present invention relates to methods and apparatus for achieving renal neuromodulation via thermal heating and/or cooling mechanisms.

BACKGROUND

Congestive Heart Failure (“CHF”) is a condition that occurs when the heart becomes damaged and reduces blood flow to the organs of the body. If blood flow decreases sufficiently, kidney function becomes altered, which results in fluid retention, abnormal hormone secretions and increased constriction of blood vessels. These results increase the workload of the heart and further decrease the capacity of the heart to pump blood through the kidneys and circulatory system.

It is believed that progressively decreasing perfusion of the kidneys is a principal non-cardiac cause perpetuating the downward spiral of CHF. Moreover, the fluid overload and associated clinical symptoms resulting from these physiologic changes result in additional hospital admissions, poor quality of life and additional costs to the health care system.

In addition to their role in the progression of CHF, the kidneys play a significant role in the progression of Chronic Renal Failure (“CRF”), End-Stage Renal Disease (“ESRD”), hypertension (pathologically high blood pressure) and other cardio-renal diseases. The functions of the kidneys can be summarized under three broad categories: filtering blood and excreting waste products generated by the body's metabolism; regulating salt, water, electrolyte and acid-base balance; and secreting hormones to maintain vital organ blood flow. Without properly functioning kidneys, a patient will suffer water retention, reduced urine flow and an accumulation of waste toxins in the blood and body. These conditions result from reduced renal function or renal failure (kidney failure) and are believed to increase the workload of the heart. In a CHF patient, renal failure will cause the heart to further deteriorate as fluids are retained and blood toxins accumulate due to the poorly functioning kidneys.

It has been established in animal models that the heart failure condition results in abnormally high sympathetic activation of the kidneys. An increase in renal sympathetic nerve activity leads to decreased removal of water and sodium from the body, as well as increased renin secretion. Increased renin secretion leads to vasoconstriction of blood vessels supplying the kidneys, which causes decreased renal blood flow. Reduction of sympathetic renal nerve activity, e.g., via denervation, may reverse these processes.

Applicants have previously described methods and apparatus for treating renal disorders by applying a pulsed electric field to neural fibers that contribute to renal function. See, for example, Applicants' U.S. Pat. Nos. (a) 7,653,438, (b) 8,145,316, and (c) 7,620,451, all of which are incorporated herein by reference in their entireties. A pulsed electric field (“PEF”) may initiate renal neuromodulation, e.g., denervation, for example, via irreversible electroporation or via electrofusion. The PEF may be delivered from apparatus positioned intravascularly, extravascularly, intra-to-extravascularly or a combination thereof. Additional methods and apparatus for achieving renal neuromodulation, e.g., via localized drug delivery (such as by a drug pump or infusion catheter) or via use of a stimulation electric field, etc, are described, for example, in Applicants' U.S. Pat. Nos. 7,162,303 and 6,978,174, both of which are incorporated herein by reference in their entireties.

A potential challenge of using PEF systems for treating renal disorders is to selectively electroporate target cells without affecting other cells. For example, it may be desirable to irreversibly electroporate renal nerve cells that travel along or in proximity to renal vasculature, but it may not be desirable to damage the smooth muscle cells of which the vasculature is composed. As a result, an overly aggressive course of PEF therapy may persistently injure the renal vasculature, but an overly conservative course of PEF therapy may not achieve the desired renal neuromodulation.

Applicants have previously described methods and apparatus for monitoring changes in tissue impedance or conductivity in order to determine the effects of pulsed electric field therapy, e.g., to determine an extent of electroporation and/or its degree of irreversibility. See, for example, Applicants' co-pending U.S. Patent Application Publication No. US 2007/0083239, which is incorporated herein by reference in its entirety. However, in some patients it may be difficult or impractical to achieve such real-time monitoring when utilizing pulsed electric field neuromodulatory mechanisms. In some patients, this may necessitate re-intervention should it be established after the procedure that a degree of induced neuromodulation was not sufficient to achieve a desired treatment outcome. Thus, it would be desirable to achieve renal neuromodulation via more easily monitored and/or controlled neuromodulatory mechanisms.

BRIEF DESCRIPTION OF THE DRAWINGS

Several embodiments of the present invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:

FIG. 1 is a schematic view illustrating human renal anatomy.

FIG. 2 is a schematic isometric detail view showing the location of the renal nerves relative to the renal artery.

FIG. 3 is a schematic side view, partially in section, illustrating an example of an extravascular method and apparatus for thermal renal neuromodulation.

FIGS. 4A and 4B are schematic side views, partially in section, illustrating examples of intravascular methods and apparatus for thermal renal neuromodulation.

FIGS. 5A and 5B are schematic side views, partially in section, illustrating an alternative embodiment of the intravascular methods and apparatus of FIGS. 4 comprising wall-contacting electrodes.

FIGS. 6A and 6B are schematic side views, partially in section, illustrating an additional alternative embodiment of the intravascular methods and apparatus of FIGS. 4 comprising alternative wall-contacting electrodes.

FIGS. 7A and 7B are schematic side views, partially in section, illustrating other alternative embodiments of the intravascular methods and apparatus of FIGS. 4 comprising multiple wall-contacting electrodes.

FIG. 8 is a schematic side view, partially in section, illustrating an example of an intra-to-extravascular method and apparatus for thermal renal neuromodulation.

FIG. 9 is a schematic side view, partially in section, of an alternative embodiment of the method and apparatus of FIG. 8 configured for thermal renal neuromodulation via direct application of thermal energy.

FIG. 10 is a schematic side view, partially in section, illustrating a method and apparatus for thermal renal neuromodulation comprising a thermoelectric element suitable for direct application of thermal energy to target neural fibers.

FIG. 11 is a schematic side view, partially in section, illustrating another method and apparatus for thermal renal neuromodulation comprising a thermoelectric element.

FIGS. 12A and 12B are schematic side views, partially in section, illustrating a method and apparatus for thermal renal neuromodulation via high-intensity focused ultrasound.

FIG. 13 is a schematic side view, partially in section, illustrating an alternative embodiment of the apparatus and method of FIG. 12.

FIGS. 14A and 14B are schematic diagrams for classifying the various types of thermal neuromodulation that may be achieved with the apparatus and methods of the present invention.

DETAILED DESCRIPTION A. Overview

The present invention provides methods and apparatus for renal neuromodulation via thermal heating and/or thermal cooling mechanisms, e.g., to achieve a reduction in renal sympathetic nerve activity. Thermally-induced (via heating and/or cooling) neuromodulation may be achieved via apparatus positioned proximate target neural fibers, for example, positioned within renal vasculature (i.e., positioned intravascularly), positioned extravascularly, positioned intra-to-extravascularly or a combination thereof. Thermal neuromodulation by either heating or cooling may be due to direct effect to, or alteration of, the neural structures that is induced by the thermal stress. Additionally or alternatively, the thermal neuromodulation may at least in part be due to alteration of vascular structures, e.g., arteries, arterioles, capillaries or veins, which perfuse the target neural fibers or surrounding tissue. Furtherstill, the modulation may at least in part be due to electroporation of the target neural fibers or of surrounding tissue.

As used herein, thermal heating mechanisms for neuromodulation include both thermal ablation and non-ablative thermal injury or damage (e.g., via sustained heating or resistive heating). Thermal heating mechanisms may include raising the temperature of target neural fibers above a desired threshold, for example, above a body temperature of about 37° C., e.g., to achieve non-ablative thermal injury, or above a temperature of about 45° C. (e.g., above about 60° C.) to achieve ablative thermal injury.

As used herein, thermal cooling mechanisms for neuromodulation include non-freezing thermal slowing of nerve conduction and/or non-freezing thermal nerve injury, as well as freezing thermal nerve injury. Thermal cooling mechanisms may include reducing the temperature of target neural fibers below a desired threshold, for example, below the body temperature of about 37° C. (e.g., below about 20° C.) to achieve non-freezing thermal injury. Thermal cooling mechanisms also may include reducing the temperature of the target neural fibers below about 0° C., e.g., to achieve freezing thermal injury.

In addition to monitoring or controlling the temperature during thermal neuromodulation, a length of exposure to thermal stimuli may be specified to affect an extent or degree of efficacy of the thermal neuromodulation. The length of exposure to thermal stimuli is longer than instantaneous exposure, such as longer than about 30 seconds, or even longer than 2 minutes. Furthermore, the length of exposure can be less than 10 minutes, though this should in no way be construed as the upper limit of the exposure period. Exposure times measured in hours, days or longer, may be utilized to achieve desired thermal neuromodulation.

When conducting neuromodulation via thermal mechanisms, the temperature threshold discussed previously may be determined as a function of the duration of exposure to thermal stimuli. Additionally or alternatively, the length of exposure may be determined as a function of the desired temperature threshold. These and other parameters may be specified or calculated to achieve and control desired thermal neuromodulation.

In some embodiments, thermally-induced renal neuromodulation may be achieved via direct application of thermal cooling or heating energy to the target neural fibers. For example, a chilled or heated fluid can be applied at least proximate to the target neural fiber, or heated or cooled elements (e.g., a thermoelectric element or a resistive heating element) can be placed in the vicinity of the neural fibers. In other embodiments, thermally-induced renal neuromodulation may be achieved via indirect generation and/or application of the thermal energy to the target neural fibers, such as through application of a ‘thermal’ electric field, of high-intensity focused ultrasound, of laser irradiation, etc., to the target neural fibers. For example, thermally-induced renal neuromodulation may be achieved via delivery of a pulsed or continuous thermal electric field to the target neural fibers, the electric field being of sufficient magnitude and/or duration to thermally induce the neuromodulation in the target fibers (e.g., to heat or thermally ablate or necrose the fibers). Additional and alternative methods and apparatus may be utilized to achieve thermally-induced renal neuromodulation, as described hereinafter.

When utilizing thermal heating mechanisms for thermal neuromodulation, protective cooling elements, such as convective cooling elements, optionally may be utilized to protect smooth muscle cells or other non-target tissue from thermal damage during the thermally-induced renal neuromodulation. Likewise, when utilizing thermal cooling mechanisms, protective heating elements, such as convective heating elements, may be utilized to protect the non-target tissue. When thermal neuromodulation is achieved via thermal energy delivered intravascularly, the non-target tissue may be protected by utilizing blood flow as a conductive and/or convective heat sink that carries away excess thermal energy (hot or cold). For example, when blood flow is not blocked, the circulating blood may provide a relatively constant temperature medium for removing the excess thermal energy from the non-target tissue during the procedure. The non-target tissue additionally or alternatively may be protected by focusing the thermal heating or cooling energy on the target neural fibers such that an intensity of the thermal energy is insufficient to induce the thermal damage in the non-target tissue distant from the target neural fibers.

In some embodiments, methods and apparatus for real-time monitoring of an extent or degree of neuromodulation or denervation (e.g., an extent or degree of thermal damage) in the target neural fibers and/or of thermal damage in the non-target tissue may be provided. Likewise, real-time monitoring of the thermal energy delivery element may be provided. Such methods and apparatus may, for example, comprise a thermocouple or other temperature sensor for measuring the temperature of the monitored tissue or of the thermal energy delivery element. Power or total energy delivered additionally or alternatively may be monitored.

To better understand the structures of devices of the present invention and the methods of using such devices for thermally-induce renal neuromodulation, it is instructive to examine the renal anatomy in humans.

B. Renal Anatomy Summary

With reference to FIG. 1, the human renal anatomy includes the kidneys K, which are supplied with oxygenated blood by the renal arteries RA. The renal arteries are connected to the heart via the abdominal aorta AA. Deoxygenated blood flows from the kidneys to the heart via the renal veins RV and the inferior vena cava IVC.

FIG. 2 illustrates a portion of the renal anatomy in greater detail. More specifically, the renal anatomy also includes renal nerves RN extending longitudinally along the lengthwise dimension L of renal artery RA, generally within the adventitia of the artery. The renal artery RA has smooth muscle cells SMC that surround the arterial circumference and spiral around the angular axis θ of the artery. The smooth muscle cells of the renal artery accordingly have a lengthwise or longer dimension extending transverse (i.e., non-parallel) to the lengthwise dimension of the renal artery. The misalignment of the lengthwise dimensions of the renal nerves and the smooth muscle cells is defined as “cellular misalignment.”

C. Embodiments of Apparatus and Methods for Neuromodulation

FIGS. 3-13 illustrate examples of systems and methods for thermally-induced renal neuromodulation. FIG. 3 shows one embodiment of an extravascular apparatus 200 that includes one or more electrodes configured to deliver a thermal electric field to renal neural fibers in order to achieve renal neuromodulation via heating. The apparatus of FIG. 3 is configured for temporary extravascular placement; however, it should be understood that partially or completely implantable extravascular apparatus additionally or alternatively may be utilized. Applicants have previously described extravascular pulsed electric field systems, for example, in Applicants' U.S. Pat. No. 8,145,316, which has been incorporated herein by reference in its entirety.

In FIG. 3, apparatus 200 comprises a laparoscopic or percutaneous system having a probe 210 configured for insertion in proximity to the track of the renal neural supply along the renal artery or vein or hilum and/or within Gerota's fascia under, e.g., CT or radiographic guidance. At least one electrode 212 is configured for delivery through the probe 210 to a treatment site for delivery of a thermal electric field therapy. The electrode(s) 212, for example, may be mounted on a catheter and electrically coupled to a thermal electric field generator 50 via wires 211. In an alternative embodiment, a distal section of the probe 210 may have at least one electrode 212, and the probe may have an electrical connector to couple the probe to the field generator 50 for delivering a thermal electric field to the electrode(s) 212.

The field generator 50 is located external to the patient. The generator, as well as any of the electrode embodiments described herein, may be utilized with any embodiment of the present invention for delivery of a thermal electric field with desired field parameters, e.g., parameters sufficient to thermally or otherwise induce renal neuromodulation in target neural fibers via heating and/or electroporation. It should be understood that electrodes of embodiments described hereinafter may be electrically connected to the generator even though the generator is not explicitly shown or described with each embodiment. Furthermore, the field generator optionally may be positioned internal to the patient. Furtherstill, the field generator may additionally comprise or may be substituted with an alternative thermal energy generator, such as a thermoelectric generator for heating or cooling (e.g., a Peltier device), or a thermal fluid injection system for heating or cooling, etc.

The electrode(s) 212 can be individual electrodes that are electrically independent of each other, a segmented electrode with commonly connected contacts, or a continuous electrode. A segmented electrode may, for example, be formed by providing a slotted tube fitted onto the electrode, or by electrically connecting a series of individual electrodes. Individual electrodes or groups of electrodes 212 may be configured to provide a bipolar signal. The electrodes 212 may be dynamically assignable to facilitate monopolar and/or bipolar energy delivery between any of the electrodes and/or between any of the electrodes and an external ground pad. Such a ground pad may, for example, be attached externally to the patient's skin, e.g., to the patient's leg or flank. In FIG. 3, the electrodes 212 comprise a bipolar electrode pair. The probe 210 and the electrodes 212 may be similar to the standard needle or trocar-type used clinically for RF nerve block. Alternatively, the apparatus 200 may comprise a flexible and/or custom-designed probe for the renal application described herein.

In FIG. 3, the percutaneous probe 210 has been advanced through a percutaneous access site P into proximity with a patient's renal artery RA. The probe pierces the patient's Gerota's fascia F, and the electrodes 212 are advanced into position through the probe and along the annular space between the patient's artery and fascia. Once properly positioned, the target neural fibers may be heated via a pulsed or continuous electric field delivered across the bipolar electrodes 212. Such heating may, for example, ablate or cause non-ablative thermal injury to the target neural fibers, thereby at least partially denervating the kidney innervated by the target neural fibers. The electric field also may induce reversible or irreversible electroporation in the target neural fibers, which may compliment the thermal injury induced in the neural fibers. After treatment, the apparatus 200 may be removed from the patient to conclude the procedure.

Referring now to FIGS. 4A and 4B, embodiments of intravascular systems for thermally-induced renal neuromodulation is described. Applicants have previously described intravascular pulsed electric field systems, for example, in U.S. Pat. No. 7,653,438, which has been incorporated herein by reference in its entirety. The embodiments of FIG. 4 include an apparatus 300 comprising a catheter 302 having an optional positioning element 304 (e.g., a balloon, an expandable wire basket, other mechanical expanders, etc.), shaft electrodes 306 a and 306 b disposed along the shaft of the catheter, and optional radiopaque markers 308 disposed along the shaft of the catheter in the region of the positioning element 304. The electrodes 306 a-b, for example, can be arranged such that the electrode 306 a is near a proximal end of the positioning element 304 and the electrode 306 b is near the distal end of the positioning element 304. The electrodes 306 are electrically coupled to the field generator 50 (see FIG. 3), which is disposed external to the patient, for delivery of a thermal electric field for heating of target neural fibers. In an alternative embodiment, one or more of the electrodes may comprise Peltier electrodes for cooling the target neural fibers to modulate the fibers.

The positioning element 304 optionally may center or otherwise position the electrodes 306 a and 306 b within a vessel. Additionally, as in FIG. 4A, the positioning element may comprise an impedance-altering element that alters the impedance between electrodes 306 a and 306 b during the therapy, for example, to better direct the thermal electric field across the vessel wall. This may reduce an energy required to achieve desired renal neuromodulation and may reduce a risk of injury to non-target tissue. Applicants have previously described use of a suitable impedance-altering element in Applicants' U.S. Pat. No. 7,756,583, which is incorporated herein by reference in its entirety. When the positioning element 304 comprises an inflatable balloon as in FIG. 4A, the balloon may serve as both a centering element for the electrodes 306 and as an impedance-altering electrical insulator for directing an electric field delivered across the electrodes, e.g., for directing the electric field into or across the vessel wall for modulation of target neural fibers. Electrical insulation provided by the positioning element 304 may reduce the magnitude of applied energy or other parameters of the thermal electric field necessary to achieve desired heating at the target fibers.

Furthermore, the positioning element 304 optionally may be utilized as a cooling element and/or a heating element. For example, the positioning element 304 may be inflated with a chilled fluid that serves as a heat sink for removing heat from tissue that contacts the element. Conversely, the positioning element 304 optionally may be a heating element by inflating it with a warmed fluid that heats tissue in contact with the element. The thermal fluid optionally may be circulated and/or exchanged within the positioning element 304 to facilitate more efficient conductive and/or convective heat transfer. Thermal fluids also may be used to achieve thermal neuromodulation via thermal cooling or heating mechanisms, as described in greater detail herein below. The positioning element 304 (or any other portion of apparatus 300) additionally or alternatively may comprise one or more sensors for monitoring the process. In one embodiment, the positioning element 304 has a wall-contacting thermocouple 310 (FIG. 4A) for monitoring the temperature or other parameters of the target tissue, the non-target tissue, the electrodes, the positioning element and/or any other portion of the apparatus 300.

The electrodes 306 can be individual electrodes (i.e., independent contacts), a segmented electrode with commonly connected contacts, or a single continuous electrode. Furthermore, the electrodes 306 may be configured to provide a bipolar signal, or the electrodes 306 may be used together or individually in conjunction with a separate patient ground pad for monopolar use. As an alternative or in addition to placement of the electrodes 306 along the central shaft of the catheter 302, as in FIG. 4, the electrodes 306 may be attached to the positioning element 304 such that they contact the wall of the renal artery RA. In such a variation, the electrodes may, for example, be affixed to the inside surface, outside surface or at least partially embedded within the wall of the positioning element. FIG. 5 illustrate alternative wall-contacting electrodes.

In use, the catheter 302 may be delivered to the renal artery RA as shown, or it may be delivered to a renal vein or to any other vessel in proximity to neural tissue contributing to renal function, in a low profile delivery configuration through a guide catheter or other device. Alternatively, catheters may be positioned in multiple vessels for thermal renal neuromodulation, e.g., within both the renal artery and the renal vein. Multi-vessel techniques for pulsed electric field renal neuromodulation have been described previously, for example, in Applicants' U.S. Pat. No. 7,853,333, which is incorporated herein by reference in its entirety.

Once positioned within the renal vasculature as desired, the optional positioning element 304 may be expanded into contact with an interior wall of the vessel. A thermal electric field then may be generated by the field generator 50, transferred through the catheter 302 to the electrodes 306, and delivered via the electrodes 306 across the wall of the artery. The electric field thermally modulates the activity along neural fibers that contribute to renal function via heating. In several embodiments, the thermal modulation at least partially denervates the kidney innervated by the neural fibers via heating. This may be achieved, for example, via thermal ablation or via non-ablative damage of the target neural fibers. The electric field also may induce electroporation in the neural fibers.

In the embodiment of FIG. 4A, the positioning element 304 illustratively comprises an inflatable balloon, which may preferentially direct the electric field as discussed. In the embodiment of FIG. 4B, the positioning element comprises an expandable wire basket that substantially centers the electrodes 306 within the vessel without blocking blood flow through the vessel. During delivery of the thermal electric field (or of other thermal energy), the blood may act as a heat sink for conductive and/or convective heat transfer for removing excess thermal energy from the non-target tissue, thereby protecting the non-target tissue. This effect may be enhanced when blood flow is not blocked during energy delivery, as in the embodiment of FIG. 4B.

Use of the patient's blood as a heat sink is expected to facilitate delivery of longer or higher energy thermal treatments with reduced risk of damage to the non-target tissue, which may enhance the efficacy of the treatment at the target neural fibers. Although the embodiment of FIG. 4B illustratively comprises a positioning element for centering the electrodes without blocking flow, it should be understood that the positioning element may be eliminated and/or that the electrodes may be attached to the positioning element such that they are not centered in the vessel upon expansion of the centering element. In such embodiments, the patient's blood may still mitigate excess thermal heating or cooling to protect non-target tissues.

In addition or as an alternative to utilizing the patient's blood as a heat sink, a thermal fluid (hot or cold) may be injected into the vessel to remove excess thermal energy and protect the non-target tissues. The thermal fluid may, for example, be injected through the device catheter or through a guide catheter at a location upstream from an energy delivery element or at other locations relative to the tissue for which protection is sought. Furthermore, this method of using an injected thermal fluid to remove excess thermal energy from non-target tissues to protect the non-target tissues from thermal injury during therapeutic treatment of target tissues may be utilized in body lumens other than blood vessels.

One or more sensors, such as the thermocouple 310 of FIG. 4A, may be used to monitor the temperature(s) or other parameter(s) at the electrodes 306, at the wall of the vessel and/or at other desired locations along the apparatus or the patient's anatomy. The thermal neuromodulation may be controlled using the measured parameter(s) as feedback. This feedback may be used, for example, to maintain the parameter(s) below a desired threshold. For example, the parameter(s) may be maintained below a threshold that may cause injury to the non-target tissues. With blood flowing through the vessel, more thermal energy may be carried away, which may allow for longer or higher energy treatments than when blood flow is blocked in the vessel.

As discussed, when utilizing intravascular apparatus to achieve thermal neuromodulation, in addition or as an alternative to central positioning of the electrode(s) within a blood vessel, the electrode(s) optionally may be configured to contact an internal wall of the blood vessel. Wall-contacting electrode(s) may facilitate more efficient transfer of a thermal electric field across the vessel wall to target neural fibers, as compared to centrally-positioned electrode(s). In some embodiments, the wall-contacting electrode(s) may be delivered to the vessel treatment site in a reduced profile configuration, then expanded in vivo to a deployed configuration wherein the electrode(s) contact the vessel wall. In some embodiments, expansion of the electrode(s) is at least partially reversible to facilitate retrieval of the electrode(s) from the patient's vessel.

FIGS. 5A and 5B depict an illustrative embodiment of intravascular apparatus having electrodes configured to contact the interior wall of a vessel. The apparatus of FIGS. 5A and 5B is an alternative embodiment of the apparatus 300 of FIGS. 4A and 4B wherein the proximal electrode 306 a of FIGS. 4A and 4B has been replaced with wall-contacting electrode 306 a′. The wall-contacting electrode comprises proximal attachment 312 a that connects the electrode to the shaft of the catheter 302 and is electrically coupled to the pulse generator. Extensions 314 a extend from proximal attachment 312 a and at least partially extend over a surface of positioning element 304. The extensions 314 a optionally may be selectively insulated such that only a selective portion of the extensions, e.g., the distal tips of the extensions, are electrically active. The electrode 306 a′ optionally may be fabricated from a slotted tube, such as a stainless steel or shape-memory (e.g., NiTi) slotted tube. Furthermore, all or a portion of the electrode may be gold-plated to improve radiopacity and/or conductivity.

As seen in FIG. 5A, catheter 302 may be delivered over a guidewire G to a treatment site within the patient's vessel with the electrode 306 a′ positioned in a reduced profile configuration. Catheter 302 optionally may be delivered through a guide catheter 303 to facilitate such reduced profile delivery of the wall-contacting electrode. When positioned as desired at a treatment site, the electrode may be expanded into contact with the vessel wall by expanding the optional positioning element 304, as in FIG. 5B. A thermal monopolar or bipolar electric field then may be delivered across the vessel wall and between the electrodes 306 a′ and 306 b to induce thermal neuromodulation, as discussed previously. The optional positioning element 304 may alter impedance within the blood vessel and more efficiently route the electrical energy across the vessel wall to the target neural fibers.

After delivery of the electric field, the electrode 306 a′ may be returned to a reduced profile to facilitate removal of the apparatus 300 from the patient. For example, the positioning element 304 may be collapsed (e.g., deflated), and the electrode 306 a′ may be contracted by withdrawing the catheter 302 within the guide catheter 303. Alternatively, the electrode may be fabricated from a shape-memory material biased to the collapsed configuration, such that the electrode self-collapses upon collapse of the positioning element.

Although in FIGS. 5A and 5B the electrode 306 a′ is expanded into contact with the vessel wall, it should be understood that the electrode alternatively may be fabricated from a self-expanding material biased such that the electrode self-expands into contact with the vessel wall upon positioning of the electrode distal of the guide catheter 303. A self-expanding embodiment of the electrode 306 a′ may obviate a need for the positioning element 304 and/or may facilitate maintenance of blood flow through the blood vessel during delivery of an electric field via the electrode. After delivery of the electric field, the self-expanding electrode 306 a′ may be returned to a reduced profile to facilitate removal of the apparatus 300 from the patient by withdrawing the catheter 302 within the guide catheter 303.

FIGS. 6A and 6B depict another embodiment of the apparatus and methods of FIGS. 4A and 4B comprising a wall-contacting electrode. As an alternative to the proximal attachment 312 a of electrode 306 a′ of FIGS. 5A and 5B, the electrode 306 a″ of FIG. 6 comprises distal attachment 316 a for coupling the electrode to the shaft of catheter 302 on the distal side of the positioning element 304. Distal attachment of the electrode allows the electrode to extend over the entirety of the positioning element 304 and may facilitate contraction of the electrode 306 a″ after thermal neuromodulation. For example, the electrode 306 a″ can be contracted by proximally retracting the extensions 312 a relative to the catheter 302 during or after contraction of the positioning element 304. FIG. 6A shows the electrode 306 a″ in the reduced profile configuration, while FIG. 6B shows the electrode in the expanded, wall-contacting configuration.

FIGS. 7A and 7B show additional alternative embodiments of the methods and apparatus of FIGS. 4A and 4B. In FIGS. 7A and 7B, the apparatus 300 comprises both the proximal electrode 306 a′ of FIGS. 5A and 5B, as well as a wall-contacting distal electrode 306 b′. The embodiment of FIG. 7A comprises proximal and distal positioning elements 304 a and 304 b, respectively, for expanding the proximal and distal wall-contacting electrodes 306 a′ and 306 b′, respectively, into contact with the vessel wall. The embodiment of FIG. 7B comprises only a single positioning element 304, but the distal wall-contacting electrode 306 b′ is proximal facing and positioned over the distal portion of the positioning element 304 to facilitate expansion of the distal electrode 306 b′. In the embodiment of FIG. 7B, the extensions of the proximal and distal electrodes optionally may be connected along non-conductive connectors 318 to facilitate collapse and retrieval of the electrodes post-treatment.

A bipolar electric field may be delivered between the proximal and distal wall-contacting electrodes, or a monopolar electric field may be delivered between the proximal and/or distal electrode(s) and an external ground. Having both the proximal and distal electrodes in contact with the wall of the vessel may facilitate more efficient energy transfer across the wall during delivery of a thermal electric field, as compared to having one or both of the proximal and distal electrodes centered within the vessel.

In addition to extravascular and intravascular systems for thermally-induced renal neuromodulation, intra-to-extravascular systems may be provided. The intra-to-extravascular systems may, for example, have electrode(s) that are delivered to an intravascular position, and then at least partially passed through/across the vessel wall to an extravascular position prior to delivery of a thermal electric field. Intra-to-extravascular positioning of the electrode(s) may place the electrode(s) in closer proximity to target neural fibers for delivery of a thermal electric field, as compared to fully intravascular positioning of the electrode(s). Applicants have previously described intra-to-extravascular pulsed electric field systems, for example, in Applicants' U.S. Pat. No. 7,620,451, which is incorporated herein by reference in its entirety.

With reference to FIG. 8, one embodiment of an intra-to-extravascular (“ITEV”) system for thermally-induced renal neuromodulation is described. ITEV system 320 comprises a catheter 322 having (a) a plurality of proximal electrode lumens terminating at proximal side ports 324, (b) a plurality of distal electrode lumens terminating at distal side ports 326, and (c) a guidewire lumen 323. The catheter 322 preferably comprises an equal number of proximal and distal electrode lumens and side ports. The system 320 also includes proximal needle electrodes 328 that may be advanced through the proximal electrode lumens and the proximal side ports 324, as well as distal needle electrodes 329 that may be advanced through the distal electrode lumens and the distal side ports 326.

Catheter 322 comprises an optional expandable positioning element 330, which may comprise an inflatable balloon or an expandable basket or cage. In use, the positioning element 330 may be expanded prior to deployment of the needle electrodes 328 and 329 in order to position or center the catheter 322 within the patient's vessel (e.g., within renal artery RA). Centering the catheter 322 is expected to facilitate delivery of all needle electrodes to desired depths within/external to the patient's vessel (e.g., to deliver all of the needle electrodes approximately to the same depth). In FIG. 8, the illustrated positioning element 330 is positioned between the proximal side ports 324 and the distal side ports 326, i.e., between the delivery positions of the proximal and distal electrodes. However, it should be understood that the positioning element 330 additionally or alternatively may be positioned at a different location or at multiple locations along the length of the catheter 322 (e.g., at a location proximal of the side ports 324 and/or at a location distal of the side ports 326).

As illustrated in FIG. 8, the catheter 322 may be advanced to a treatment site within the patient's vasculature (e.g., to a treatment site within the patient's renal artery RA) over a guidewire (not shown) via the lumen 323. During intravascular delivery, the electrodes 328 and 329 may be positioned such that their non-insulated and sharpened distal regions are positioned within the proximal and distal lumens, respectively. Once positioned at a treatment site, a medical practitioner may advance the electrodes via their proximal regions that are located external to the patient. Such advancement causes the distal regions of the electrodes 328 and 329 to exit side ports 324 and 326, respectively, and pierce the wall of the patient's vasculature such that the electrodes are positioned extravascularly via an ITEV approach.

The proximal electrodes 328 can be connected to electric field generator 50 as active electrodes, and the distal electrodes 329 can serve as return electrodes. In this manner, the proximal and distal electrodes form bipolar electrode pairs that align the thermal electric field with a longitudinal axis or direction of the patient's vasculature. As will be apparent, the distal electrodes 329 alternatively may comprise the active electrodes and the proximal electrodes 328 may comprise the return electrodes. Furthermore, the proximal and/or the distal electrodes may comprise both active and return electrodes. Furtherstill, the proximal and/or the distal electrodes may be utilized in combination with an external ground for delivery of a monopolar thermal electric field. Any combination of active and distal electrodes may be utilized, as desired.

When the electrodes 328 and 329 are connected to generator 50 and positioned extravascularly, and with the positioning element 330 optionally expanded, delivery of the thermal electric field may proceed to achieve desired renal neuromodulation via heating. The electric field also may induce electroporation. After achievement of the thermally-induced renal neuromodulation, the electrodes may be retracted within the proximal and distal lumens, and the positioning element 330 may be collapsed for retrieval. ITEV system 320 then may be removed from the patient to complete the procedure. Additionally or alternatively, the system may be repositioned to provide therapy at another treatment site, such as to provide bilateral renal neuromodulation.

As discussed previously, cooling elements, such as convective cooling elements, may be utilized to protect non-target tissues like smooth muscle cells from thermal damage during thermally-induced renal neuromodulation via heat generation. Non-target tissues additionally or alternatively may be protected by focusing the thermal energy on the target neural fibers such that an intensity of the thermal energy is insufficient to induce thermal damage in non-target tissues distant from the target neural fibers.

Although FIGS. 3-8 illustratively show bipolar apparatus, it should be understood that monopolar apparatus alternatively may be utilized. For example, an active monopolar electrode may be positioned intravascularly, extravascularly or intra-to-extravascularly in proximity to target neural fibers that contribute to renal function. A return electrode ground pad may be attached to the exterior of the patient. Finally, a thermal electric field may be delivered between the in vivo monopolar electrode and the ex vivo ground pad to effectuate desired thermally-induced renal neuromodulation. Monopolar apparatus additionally may be utilized for bilateral renal neuromodulation.

The embodiments of FIGS. 3-8 illustratively describe methods and apparatus for thermally-induced renal neuromodulation via delivery of thermal electric fields that modulate the target neural fibers. However, it should be understood that alternative methods and apparatus for thermally-induced (via both heating and cooling) renal neuromodulation may be provided. For example, electric fields may be used to cool and modulate the neural fibers, e.g., via thermoelectric or Peltier elements. Thermally-induced renal neuromodulation optionally may be achieved via direct application of thermal energy to the target neural fibers. Such direct thermal energy may be generated and/or transferred in a variety of ways, such as via resistive heating, via delivery of a heated or chilled fluid (see FIGS. 9 and 11), via a Peltier element (see FIG. 10), etc. Thermally-induced renal neuromodulation additionally or alternatively may be achieved via application of high-intensity focused ultrasound to the target neural fibers (see FIG. 12). Additional and alternative methods and apparatus for thermally-induced renal neuromodulation may be used in accordance with the present invention.

With reference now to FIG. 9, an alternative embodiment of the apparatus and methods of FIG. 8 is described that is configured for thermally-induced neuromodulation via direct application of thermal energy. In the embodiment of FIG. 9, the electrodes 328 and 329 of FIG. 8 have been replaced with infusion needles 328′ and 329′, respectively. A thermal fluid F may be delivered through the needles to the target neural fibers. The thermal fluid may be heated in order to raise the temperature of the target neural fibers above a desired threshold. For example, the temperature of the neural fibers can be raised above a body temperature of about 37° C., or above a temperature of about 45° C. Alternatively, the thermal fluid may be chilled to reduce the temperature of the target neural fibers below a desired threshold. For example, the neural fibers can be cooled to below the body temperature of about 37° C., or further cooled below about 20° C., or still further cooled below a freezing temperature of about 0° C. As will be apparent, in addition to intra-to-extravascular delivery of a thermal fluid, the thermal fluid may be delivered intravascularly (e.g., may inflate and/or be circulated through a balloon member), extravascularly (e.g., may be circulated through a vascular cuff) or a combination thereof.

In addition or as alternative to injection of a thermal fluid to the target neural fibers through infusion needles 328′ and 329′, an alternative neuromodulatory agent, such as a drug or medicament, may be injected to modulate, necrose or otherwise block or reduce transmission along the target neural fibers. Examples of alternative neuromodulatory agents include, but are not limited to, phenol and neurotoxins, such as botulinum toxin. Additional neuromodulatory agents, per se known, will be apparent to those of skill in the art.

FIG. 10 shows another method and apparatus for thermal renal neuromodulation via direct application of thermal energy to the target neural fibers. The apparatus 340 comprises renal artery cuff 342 having one or more integrated thermoelectric elements that are electrically coupled to an internal or external power supply 344. The thermoelectric element utilizes the well-known Peltier effect (i.e., the establishment of a thermal gradient induced by an electric voltage) to achieve thermal renal neuromodulation.

An electric current is passed from the power supply to the thermoelectric element, which comprises two different metals (e.g., a p-type and an n-type semiconductor) that are connected to each other at two junctions. The current induces a thermal gradient between the two junctions, such that one junction cools while the other is heated. Reversal of the polarity of the voltage applied across the two junctions reverses the direction of the thermal gradient.

Either the hot side or the cold side of the thermoelectric element faces radially inward in order to heat or cool, respectively, the target neural fibers that travel along the renal artery to achieve thermal renal neuromodulation. Optionally, the radially outward surface of the thermoelectric element may be insulated to reduce a risk of thermal damage to the non-target tissues. The cuff 342 may comprise one or more temperature sensors, such as thermocouples, for monitoring the temperature of the target neural fibers and/or of the non-target tissues.

FIG. 11 shows another method and apparatus utilizing the Peltier effect. The apparatus 350 comprises an implanted or external pump 352 connected to a renal artery cuff 354 via inlet fluid conduit 356 a and outlet fluid conduit 356 b. The inlet fluid conduit transfers fluid from the pump to the cuff, while the outlet fluid conduit transfers fluid from the cuff to the pump to circulate fluid through the cuff. A reservoir of fluid may be located in the cuff, the pump and/or in the fluid conduits.

The pump 352 further comprises one or more thermoelectric or other thermal elements in heat exchange contact with the fluid reservoir for cooling or heating the fluid that is transferred to the cuff to thermally modulate the target neural fibers. The apparatus 350 optionally may have controls for automatic or manual control of fluid heating or cooling, as well as fluid circulation within the cuff. Furthermore, the apparatus may comprise temperature and/or renal sympathetic neural activity monitoring or feedback control. Although the apparatus illustratively is shown unilaterally treating neural fibers innervating a single kidney, it should be understood that bilateral treatment of neural fibers innervating both kidneys alternatively may be provided.

Thermal renal neuromodulation alternatively may be achieved via high-intensity focused ultrasound, either pulsed or continuous. High intensity focused ultrasound also may induce reversible or irreversible electroporation in the target neural fibers. Furthermore, the ultrasound may be delivered over a full 360° (e.g. when delivered intravascularly) or over a radial segment of less than 360° (e.g., when delivered intravascularly, extravascularly, intra-to-extravascularly, or a combination thereof). In FIG. 12, the apparatus 360 comprises a catheter 362 having ultrasound transducers 364 positioned along the shaft of the catheter within an inflatable balloon 366. The ultrasound transducers are coupled to an ultrasound signal generator via conductors 365. The balloon comprises an acoustically reflective portion 368 of a surface of the balloon for reflecting an ultrasound wave, as well as an acoustically transmissive portion 369 of the surface for passage of the wave through the balloon. In this manner, the wave may be focused as shown at a focal point or radius P positioned a desired focal distance from the catheter shaft. In an alternative embodiment, the transducers may be attached directly to the balloon.

The focal distance may be specified or dynamically variable such that, when positioned within a blood vessel, the ultrasonic wave is focused at a desired depth on target neural fibers outside of the vessel. For example, a family of catheter sizes may be provided to allow for a range of specified focal distances. A dynamically variable focal distance may be achieved, for example, via calibrated expansion of the balloon.

Focusing the ultrasound wave may produce a reverse thermal gradient that protects the non-target tissues and selectively affect the target neural fibers to achieve thermal renal neuromodulation via heating. As a result, the temperature at the vessel wall may be less than the temperature at the target tissue. FIG. 12A shows the apparatus 360 in a reduced delivery and retrieval configuration, while FIG. 12B shows the apparatus in an expanded deployed configuration. FIG. 13 shows an alternative embodiment of the apparatus 360 wherein the ultrasound transducers 364′ are concave, such that the ultrasound signal is self-focusing without need of the reflective portion of the balloon 366 (e.g., the balloon may be acoustically transmissive at all points).

The apparatus described above with respect to FIGS. 3-13 optionally may be used to quantify the efficacy, extent or cell selectivity of thermally-induced renal neuromodulation in order to monitor and/or control the neuromodulation. As discussed previously, the apparatus may further comprise one or more sensors, such as thermocouples or imaging transducers, for measuring and monitoring one or more parameters of the apparatus, of the target neural fibers and/or of the non-target tissues. For example, a temperature rise or drop above or below certain thresholds is expected to thermally ablate, non-ablatively injure, freeze or otherwise damage the target neural fibers, thereby modulating the target neural fibers.

FIGS. 14A and 14B classify the various types of thermal neuromodulation that may be achieved with the apparatus and methods of the present invention. FIGS. 14A and 14B are provided only for the sake of illustration and should in no way be construed as limiting. FIG. 14A classifies thermal neuromodulation due to heat exposure. As shown, exposure to heat in excess of a body temperature of about 37° C., but below a temperature of about 45° C., may induce thermal injury via moderate heating of the target neural fibers or of vascular structures that perfuse the target fibers. For example, this may induce non-ablative thermal injury in the fibers or structures. Exposure to heat above a temperature of about 45° C., or above about 60° C., may induce thermal injury via substantial heating of the fibers or structures. For example, such higher temperatures may thermally ablate the target neural fibers or the vascular structures. Regardless of the type of heat exposure utilized to induce the thermal neuromodulation, a reduction in renal sympathetic nerve activity (“RSNA”) is expected.

As seen in FIG. 14B, thermal cooling for neuromodulation includes non-freezing thermal slowing of nerve conduction and/or nerve injury, as well as freezing thermal nerve injury. Non-freezing thermal cooling may include reducing the temperature of the target neural fibers or of the vascular structures that feed the fibers to temperatures below the body temperature of about 37° C., or below about 20° C., but above the freezing temperature of about 0° C. This non-freezing thermal cooling may either slow nerve conduction or may cause direct neural injury. Slowed nerve conduction may imply continuous or intermittent cooling of the target neural fibers to sustain the desired thermal neuromodulation, while direct neural injury may require only a discrete treatment to achieve sustained thermal neuromodulation. Thermal cooling for neuromodulation also may include freezing thermal nerve injury, e.g., reducing the temperature of the target neural fibers or of the vascular structures that feed the fibers to temperatures below the freezing point of about 0° C. Regardless of the type of cold exposure utilized to induce the thermal neuromodulation (freezing or non-freezing), a reduction in renal sympathetic nerve activity (“RSNA”) is expected.

It is expected that thermally-induced renal neuromodulation, whether delivered extravascularly, intravascularly, intra-to-extravascularly or a combination thereof, may alleviate clinical symptoms of CHF, hypertension, renal disease, myocardial infarction, atrial fibrillation, contrast nephropathy and/or other cardio-renal diseases for a period of months, potentially up to six months or more. This time period may be sufficient to allow the body to heal; for example, this period may, reduce the risk of CHF onset after an acute myocardial infarction, thereby alleviating a need for subsequent re-treatment. Alternatively, as symptoms reoccur, or at regularly scheduled intervals, the patient may receive repeat therapy.

Although preferred illustrative variations of the present invention are described above, it will be apparent to those skilled in the art that various changes and modifications may be made thereto without departing from the invention. It is intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the invention. 

1. An ultrasound apparatus for thermally-induced renal neuromodulation, the apparatus comprising: a catheter configured for intravascular placement within a renal blood vessel of a human patient; and one or more ultrasound transducers positioned along the catheter, wherein the one or more ultrasound transducers are configured to transmit ultrasound waves to renal neural fibers outside of the vessel to achieve thermal renal neuromodulation via heating.
 2. The apparatus of claim 1, further comprising an inflatable balloon proximate to the one or more ultrasound transducers, wherein the apparatus is configured to vary between a reduced delivery and retrieval configuration and an expanded deployed configuration.
 3. The apparatus of claim 2 wherein the one or more ultrasound transducers are positioned within the inflatable balloon.
 4. The apparatus of claim 2 wherein the one or more ultrasound transducers are attached directly to the inflatable balloon.
 5. The apparatus of claim 2 wherein the inflatable balloon comprises an acoustically transmissive portion through which the ultrasound waves passes.
 6. The apparatus of claim 2 wherein the inflatable balloon comprises an acoustically reflective portion for reflecting the ultrasound waves.
 7. The apparatus of claim 2 wherein calibrated expansion of the inflatable balloon dynamically varies a focal distance of the ultrasound waves.
 8. The apparatus of claim 1 wherein the one or more ultrasound transducers are configured to delivery high intensity focused ultrasound to the neural fibers.
 9. The apparatus of claim 1 wherein the one or more ultrasound transducers comprise a self-focusing concave transducer configured to direct the ultrasound waves to a specific focal point.
 10. The apparatus of claim 1, further comprising an ultrasound signal generator coupled to the one or more ultrasound transducers.
 11. The apparatus of claim 1, further comprising a temperature sensor.
 12. The apparatus of claim 11 wherein data from the temperature sensor is used for feedback control of the thermal neuromodulation therapy.
 13. The apparatus of claim 1 wherein the one or more ultrasound transducers are configured to focus the ultrasound waves on the neural fibers at a desired depth outside of the vessel.
 14. The apparatus of claim 13 wherein a thermal gradient is produced when the ultrasound waves are focused on the neural fibers outside of the vessel.
 15. The apparatus of claim 13 wherein a thermal gradient is produced when the ultrasound waves are focused on the neural fibers outside of the vessel such that a temperature at a wall of the vessel is less than a temperature at the neural fibers, and wherein the reverse thermal gradient protects non-targeted tissue while selectively affecting the neural fibers.
 16. The apparatus of claim 1, further comprising an imaging transducer.
 17. The apparatus of claim 1 wherein the catheter further comprises a thermal fluid configured to remove excess thermal energy and protect non-targeted tissues.
 18. The apparatus of claim 17 wherein the catheter is configured to temporarily occlude blood flow in the vessel.
 19. The apparatus of claim 1 wherein the one or more ultrasound transducers are configured to transmit the ultrasound waves over a full 360°.
 20. A method for catheter-based renal neuromodulation, the method comprising: positioning a catheter having a therapeutic element within a renal blood vessel of a human patient and proximate to neural fibers associated with renal function, wherein the therapeutic element comprises one or more ultrasound transducers positioned along the catheter; and thermally inhibiting neural activity along the neural fibers via ultrasound energy from the therapeutic element.
 21. The method of claim 20 wherein positioning a catheter having a therapeutic element within a renal blood vessel comprises intravascularly positioning the catheter having the one or more ultrasound transducers within a renal artery of the patient.
 22. The method of claim 20 wherein thermally inhibiting neural activity along the neural fiber comprises delivering ultrasound energy via the one or more ultrasound transducers to a renal nerve proximate to a renal artery of the patient.
 23. The method of claim 22 wherein transferring ultrasound energy via the one or more ultrasound transducers to the renal nerve of the patient comprises transmitting the ultrasound waves over a full 360° about the catheter.
 24. The method of claim 20 wherein thermally inhibiting neural activity along the neural fiber comprises blocking neural traffic to and/or from a kidney of the patient.
 25. The method of claim 20 wherein thermally inhibiting neural activity along the neural fiber comprises ablating a renal nerve of the patient via ultrasound energy from the one or more ultrasound transducers.
 26. The method of claim 20 wherein the catheter comprises an inflatable balloon proximate to the one or more ultrasound transducers, and wherein positioning a catheter having a therapeutic element within a renal blood vessel comprises intravascularly delivering the inflatable balloon to the renal blood vessel in a reduced delivery and retrieval configuration and expanding the balloon to a deployed configuration within the renal blood vessel. 